> \definemeasure[h1][1.2\measured{w1}+26mm]
> \definemeasure[h2][1.2\measured{w2}+26mm]

\measured gives me this error (*Undefined control sequence*):

*\17>>h1 ^^@-1.2\measured*
*                       {w1}+26mm*
*\measure ...sname \csname \??measure #1\endcsname*
*                                                  \else \zeropoint \fi*
*\page_layouts_synchronize ...tparameter \c!height*
*                                                  }\ifx
\p_page_layouts_heig...*
*<inserted text> ...yout \previouslayout \page_layouts_synchronize*
*                                                  \page_layouts_check_next
\...*
*\setup_layout ...out :}[#1]\the \everysetuplayout*
*                                                  \the \everyswitchlayout
\l...*
*\syst_helpers_double_empty_one_spaced ...1[{#2}][]*

I am using ConTeXt  ver: 2013.04.20. So I tried to use \dimexpr:

\definemeasure[h1][\the\dimexpr 1.2\measure{w1}+26mm\relax]
\definemeasure[h2][\the\dimexpr 1.2\measure{w2}+26mm\relax]

but it gives me this error (there is a problem with the decimal point in
1.2 because there is no error when I put an integer instead):

*\17>>w1 .-0.*
*            7500\paperwidth*
*\measure ...sname \csname \??measure #1\endcsname*
*                                                  \else \zeropoint \fi*
*\17>>h1 r-\the \dimexpr 1.2\measure {w1}*
*                                         + 26mm \relax*
*\measure ...sname \csname \??measure #1\endcsname*
*                                                  \else \zeropoint \fi*
*\page_layouts_synchronize ...tparameter \c!height*
*                                                  }\ifx
\p_page_layouts_heig...*